Materials technology advancement program for expandable manned space structures Final report

Composite materials tests for expandable manned space structures including flammability, micrometeoroid impact, thermal shock, and tear, puncture, and fungus resistanc

Materials technology advancement program for expandable manned space structures Summary report

Composite materials testing for fire resistant wall structures for expandable manned space structure

Ultrasonic detection of flaws in fusion butt welds

Reliable and accurate Delta technique, a nondestructive ultrasonics method, uses redirection of energy to detect randomly oriented imperfections in fusion butt welds. Data on flaws can be read from either an oscilloscope or a printout

Studies of surface two-dimensional photonic band-gap structures

Two-dimensional (2D) surface photonic band-gap (SPBG) structures can be obtained by providing a shallow corrugation of the inner surface of a waveguide wall. It can be used as a distributed mirror, a cavity, or a filter in integrated optics or microwave electronics. These structures can also be an alternative to conventional 2D PBG or 1D Bragg structures. In this article, we present the results of theoretical and experimental studies of 2D SPBG structures. Data obtained from experiments are compared with theoretical results and good agreement between theory and experiment is demonstrated. Comparison of a coaxial 2D SPBG structure with a conventional 1D Bragg structure is also presented

Domain Coarsening in Systems Far from Equilibrium

The growth of domains of stripes evolving from random initial conditions is studied in numerical simulations of models of systems far from equilibrium such as Rayleigh-Benard convection. The scaling of the size of the domains deduced from the inverse width of the Fourier spectrum is studied for both potential and nonpotential models. The morphology of the domains and the defect structures are however quite different in the two cases, and evidence is presented for a second length scale in the nonpotential case.Comment: 11 pages, RevTeX; 3 uufiles encoded postscript figures appende

Theory and simulations of a gyrotron backward wave oscillator using a helical interaction waveguide

A gyrotron backward wave oscillator (gyro-BWO) with a helically corrugated interaction waveguide demonstrated its potential as a powerful microwave source with high efficiency and a wide frequency tuning range. This letter presents the theory describing the dispersion properties of such a waveguide and the linear beam-wave interaction. Numerical simulation results using the PIC code MAGIC were found to be in excellent agreement with the output measured from a gyro-BWO experiment

Laboratory Tests of Gravitational Physics Using a Cryogenic Torsion Pendulum

Progress and plans are reported for a program of gravitational physics experiments using cryogenic torsion pendula undergoing large amplitude torsional oscillation. The program includes a UC Irvine project to measure the gravitational constant G and joint UC Irvine - U. Washington projects to test the gravitational inverse square law at a range of about 10 cm and to test the weak equivalence principle.Comment: 17 pages, 11 figures, contribution to the 10th Marcel Grossman Conference Proceedings (Rio de Janeiro, July 20 - 26, 2003) - changed wording in first paragraph of section

Microwave pulse compression using a helically corrugated waveguide

There has been a drive in recent years to produce ultrahigh power short microwave pulses for a range of applications. These high-power pulses can be produced by microwave pulse compression. Sweep-frequency based microwave pulse compression using smooth bore hollow waveguides is one technique of passive pulse compression, however, at very high powers, this method has some limitation due to its operation close to cutoff. A special helical corrugation of a circular waveguide ensures an eigenwave with strongly frequency dependent group velocity far from cutoff, which makes the helically corrugated waveguide attractive for use as a passive pulse compressor for very high-power amplifiers and oscillators. The results of proof-of-principle experiments and calculations of the wave dispersion using a particle in cell particle-in-cell (PIC) code are presented. In the experiments, a 70-ns 1-kW pulse from a conventional traveling-wave tube (TWT) was compressed in a 2-m-long helical waveguide. The compressed pulse had a peak power of 10.9 kW and duration of 3 ns. In order to find the optimum pulse compression ratio, the waveguide's dispersion characteristics must be well known. The dispersion of the helix was calculated using the PIC code Magic and verified using an experimental technique. Future work detailing plans to produce short ultrahigh power gigawatt (GW) pulses will be discussed

Influence of the Dufour effect on convection in binary gas mixtures

Linear and nonlinear properties of convection in binary fluid layers heated from below are investigated, in particular for gas parameters. A Galerkin approximation for realistic boundary conditions that describes stationary and oscillatory convection in the form of straight parallel rolls is used to determine the influence of the Dufour effect on the bifurcation behaviour of convective flow intensity, vertical heat current, and concentration mixing. The Dufour--induced changes in the bifurcation topology and the existence regimes of stationary and traveling wave convection are elucidated. To check the validity of the Galerkin results we compare with finite--difference numerical simulations of the full hydrodynamical field equations. Furthermore, we report on the scaling behaviour of linear properties of the stationary instability.Comment: 14 pages and 10 figures as uuencoded Postscript file (using uufiles